The compound 5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl]sulphinyl]-1H-benzimidazole, having the generic name omeprazole, and therapeutically acceptable alkaline salts thereof are described in EP 5129 and EP 124 495, respectively. Omeprazole and its alkaline salts are effective gastric acid secretion inhibitors, and are useful as antiulcer agents. The compounds, being sulphoxides, have an asymmetric center in the sulphur atom, i.e. exist as two optical isomers (enantiomers). It has been shown that the magnesium salt of the S-enantiomer of omeprazole has better pharmacokinetic and metabolic properties compared to omeprazole, and this is described in EP 0 652 872 B 1. As a result of this the magnesium salt of the S-enantiomer of omeprazole has an improved therapeutic profile such as a lower degree of interindividual variation.
In EP 0 773 940 B1 a process for preparation of the single enantiomers of omeprazole and structurally related sulphoxides is described. In this process, a pro-chiral sulphide is oxidised with an oxidising agent in the presence of a chiral titanium complex into the corresponding sulphoxide either as a single enantiomer or in enantiomerically enriched form.
Single enantiomers of omeprazole in neutral form are difficult to obtain in crystalline state and thus these compounds are most frequently obtained as non crystalline products. In for instance WO 92/08716 the neutral form of the R enantiomer of omeprazole is obtained as an amorphous solid and in WO 94/27988 both of the enantiomers of omeprazole—in their neutral forms—are obtained in the form of syrups or oils. In WO 94/27988 is also described the preparation of alkaline salts of the single enantiomers, which are obtainable as crystalline products. These can be purified by recrystallisation resulting in products of very high optical purity. Furthermore, optically pure salts of the S-enantiomer of omeprazole are stable towards racemization both in neutral pH and basic pH.
WO 98/28294 discloses S-omeprazole in neutral form that is in a solid state.
It would be desirable to perform the oxidation of pro-chiral sulphides yielding highly crystalline sulphoxide intermediates, thus making it possible to directly recrystallise the crude sulphoxides in its neutral form in order to increase the optical purity as well as to increase the chemical purity. The purified enantiomerically enriched sulphoxide intermediates could then be converted into the S- or R-enantiomer of omeprazole and thereafter optionally into pharmaceutically acceptable salts thereof. An advantage of such a process is that a requisite chemical and optical purification step would not involve the addition of an alkaline medium to a titanium containing reaction mixture, which process is associated with problems with the formation of inorganic titanium salts that are difficult to work with. A further advantage is if the titanium catalyzed reaction step occurs earlier in the synthesis of the enantiomerically enriched compounds thereby reducing a possible risk of contamination of the final product by titanium salts.
The present invention relates to new crystalline sulphoxides which are stable enough to be directly recrystallised, the preparation of these sulphoxides and their use as intermediates in the synthesis of S- and R-enantiomer of omeprazole.